Examination of the 2 /sup 1/A/sub 1/ states of formaldehyde and ketene including analytic configuration interaction energy first derivatives for singlet excited electronic states of the same symmetry as the ground state
Journal Article
·
· J. Chem. Phys.; (United States)
OSTI ID:5964077
In an accompanying paper by Lee, Allen, and Schaefer (J. Chem. Phys. 87, xxxx (1987)), an efficient formulation for the analytic evaluation of two-configuration self-consistent-field configuration interaction (TCSCF-CI) energy first derivatives is presented. In this paper the TCSCF-CI gradient method is adapted and applied to singlet excited electronic states of the same symmetry as the ground state. Since single-configuration self-consistent-field configuration interaction (SCF-CI) wave functions are unreliable for such electronic states due to the possibility of variational collapse, the TCSCF-CI method based on excited-state orbitals is the simplest means by which dynamical electron correlation can be incorporated effectively. Geometrical structures, excitation energies, and harmonic vibrational frequencies obtained with double-zeta plus polarization (DZP) and DZP+Rydberg (DZP+R) basis sets are reported for the 2 /sup 1/A/sub 1/ states of formaldehyde and ketene. The 2 /sup 1/A/sub 1/ state of H/sub 2/CO is found to have two distinct minima with C/sub 2//sub v/ symmetry: a (..pi --> pi..*)/sup 1/ valence minimum with r/sub e/(C--O) = 1.564 A and T/sub 0/ = 8.50 eV, and an (n..-->..3p/sub y/)/sup 1/ Rydberg minimum with r/sub e/(C--O) = 1.216 A and T/sub 0/ = 7.93 eV. Some question exists on whether the (n..-->..3p/sub y/)/sup 1/ state occurs experimentally at 8.11 or 7.96 eV, but in either case the agreement between theory and experiment is good.
- Research Organization:
- Department of Chemistry and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5964077
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 87:12; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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